The invention relates to a colour cathode ray tube including an envelope having a cone portion, a magnetic screening cone extending within the cone portion, a high-voltage contact extending through the envelope in the cone portion, and a getter assembly having a conducting strip provided with a connection portion for detachably and electrically connecting the getter assembly to the high-voltage contact.
The invention also relates to a getter assembly for use in such a cathode ray tube.
A colour cathode ray tube and a getter assembly are known from U.S. Pat. No. 4,230,966. The colour television tube described in this document comprises an envelope having a cone portion, a neck portion and a display screen. Furthermore, a magnetic screen extends within the cone portion towards the neck portion. A high-voltage contact extends through the envelope in the cone portion and a metal strip is provided for electrically connecting the magnetic screen to the high-voltage contact. One end of the metal strip is provided with a getter. The metal strip and getter form a getter assembly. The function of the getter includes maintaining a sufficiently high vacuum level and providing a long lifetime of cathodes for the colour cathode ray tube. The metal strip of the getter assembly is provided with a central hole to engage with the high-voltage contact.
During production, a so-called frittable anode getter is normally used, which can be placed together with the getter assembly before assembling or fritting a display screen to the cone portion. However, to improve the total yield of the manufacturing process for the colour television tube, a certain percentage of the colour television tubes needs to be reworked in the manufacturing process. Therefore, the getter assembly in the cone portion has to be replaced via the neck portion. To this end, an operator inserts a specially adapted tongue via the neck portion and takes the getter assembly out of the tube. Thereafter, the operator reinserts the tongue again into the tube with a fresh getter assembly, manipulates the central hole of the metal strip of the getter assembly over the high-voltage contact, and then pulls the central hole around the high-voltage contact, thereby contacting the magnetic screen with the high-voltage contact. A disadvantage of the known colour cathode ray tube is that the neck portion may be damaged when the envelope is strongly curved, as is the case with shallow colour cathode ray tubes with a flat display screen.
It is an abject of the invention to improve the yield of the manufacturing process for the colour cathode ray tube. This object is achieved by a colour cathode ray tube in which the connection portion is formed by a notch provided in the conducting strip for detachably connecting the magnetic screening cone to the high-voltage contact, and the notch directly engages the high voltage contact. During reworking of the colour cathode ray tube, an operator can now easily replace the getter assembly and attach the conducting strip to the high-voltage contact by inserting the conducting strip with a tongue via the neck portion into the cone portion, with the notch directed towards the high-voltage contact, and by sliding the conducting strip over the inner wall of the cone portion so as to engage the notch with the high-voltage contact. Providing the conducting strip with a notch on one end of the conducting strip instead of with a central hole eliminates the necessity of first positioning the hole of the conducting strip over the high-voltage contact and secondly pulling the hole around a pin of the high-voltage contact. A further advantage is that a hole in the magnetic screening cone can be dispensed with because the sliding movement of the tongue and the conducting strip can be performed in a more limited space between the inner wall of the cone portion and the magnetic screening cone. Furthermore, because of the absence of this hole, the magnetic shielding performance and also the mechanical strength of the magnetic screening cone is improved. Also, this design of the conducting strip can be shorter and allows the design of shallow cathode ray tubes. Further advantageous embodiments are defined in the dependent claims.
In a preferred embodiment of the colour cathode ray tube according to the invention the conducting strip includes a conducting spring connected transversely to the conducting strip for electrically connecting the conducting strip to the magnetic screening cone. As the contacting spring is now transversely mounted on the conducting strip, a stiff and robust contact is made with the magnetic screen and the high-voltage contact.
In a further embodiment of the colour cathode my tube according to the invention the conducting strip is provided with a ridge transverse to the longitudinal axis of the conducting strip, so that the conducting strip can be detachably secured to the high-voltage contact.
In a further embodiment of the colour cathode ray tube according to the invention the mechanical force of the conducting strip acting on the high-voltage contact is increased by providing the strip with two bends positioned on both sides of the high-voltage contact and transversely to the longitudinal axis of the conducting strip, allowing a robust contact between the magnetic screening cone and the high-voltage contact.
In another embodiment of the colour cathode ray tube according to the invention two protrusions on the inner wall of the cone portion along the contour of the conducting strip prevent rotation of the conducting strip.
In a further embodiment of the colour cathode ray rube according to the invention, where the envelope also includes a neck portion and a display screen, the inner wall of the cone portion has at least one ridge directed from the neck portion toward the display screen. The two ridges on the inner wall of the cone portion enable an operator to slide the conducting strip of the getter assembly along the inner wall towards the high-voltage contact.
In a further embodiment of the colour cathode ray tube according to the invention the inner side of the cone portion has a resistive layer. This resistive layer serves to limit the effects of a possible electric flashover in the tube on the electronic circuits of the device which incorporates the colour cathode ray tube.
In a further embodiment of the colour cathode ray tube according to the invention one end of the conducting strip has two or more tongues, whereby the electrical contact between the resistive layer as well as the mechanical contact between the high-voltage contact and the conducting strip of the getter assembly is improved.
It is a further object of the invention to provide a getter assembly which can easily be replaced.
This object is achieved by a getter assembly having a getter, and a conducting strip provided with a notch for detachably connecting a magnetic screen cone to a high-voltage contact of the cathode ray tube, the notch being arranged for directly engaging the high-voltage contact.